diff --git a/src/qrules/conservation_rules.py b/src/qrules/conservation_rules.py
index 2d25817b..8266c332 100644
--- a/src/qrules/conservation_rules.py
+++ b/src/qrules/conservation_rules.py
@@ -49,7 +49,7 @@
 from copy import deepcopy
 from functools import reduce
 from textwrap import dedent
-from typing import Any, Callable, Optional, Protocol, Union
+from typing import Any, Callable, List, Optional, Protocol, Union
 
 from attrs import define, field, frozen
 from attrs.converters import optional